The present invention pertains to stabilization of an intervertebral disc space. More particularly, the invention pertains to prosthetic intervertebral disc devices and methods for stabilizing an intervertebral disc joint while providing joint mobility.
Chronic back problems can cause pain and disability for a large segment of the population. Frequently, the cause of back pain is traceable to diseased disc material between opposing vertebrae. When the disc material is diseased, the opposing vertebrae may be inadequately supported, resulting in persistent pain.
Surgical techniques have been developed to remove the diseased disc material and fuse the joint between opposing vertebral bodies. Arthrodesis of the intervertebral joint can reduce the pain associated with movement of an intervertebral joint having diseased disc material. Generally, fusion techniques involve removal of the diseased disc, drilling a bore for receiving a spinal fusion implant and inserting the implant between the opposing vertebral bodies. Spinal fusion implants and related surgical instruments for implanting a fusion device are known and disclosed in, for example, U.S. Pat. Nos. 5,741,253; 5,658,337; 5,609,636; 5,505,732; 5,489,308; 5,489,307; 5,484,437; 5,458,638; 5,055,104; 5,026,373; 5,015,247; and 4,961,740.
One disadvantage to intervertebral disc fusion is that the relative motion between the fused vertebrae is no longer possible, causing both stiffness in the spine and difficulties in the areas above and below the fused vertebrae. Thus, one alternative to fusing a diseased intervertebral joint space is to remove the diseased disc material and replace it with a prosthetic disc. Examples of prosthetic disc devices are disclosed in, for example, U.S. Pat. Nos. 4,759,766; 4,759,769; 5,258,031; 5,401,269; 5,425,773; 5,556,431 and 5,676,701. However, while such devices may provide greater mobility when compared to fused vertebrae, the mobility permitted by most known devices does not fully account for normal vertebral biomechanics.
Accordingly, there is a continuing need for intervertebral stabilization apparatuses and methods which provide mobility at the diseased intervertebral joint space. Moreover, there is a need for intervertebral stabilization methods which mimic normal intervertebral biomechanics.
The present invention is directed to devices and methods for intervertebral stabilization which provide mobility at the diseased intervertebral joint. One advantageous feature of a device according to the invention is that it mimics normal intervertebral biomechanics by providing a variable instantaneous axis of rotation.
Throughout the specification, guidance may be provided through lists of examples. In each instance, the recited list serves only as a representative group. It is not meant, however, that the list is exclusive.
In general, an intervertebral prosthetic device (IPD) of the invention is an assembly including a first member for contacting a first vertebrae, a second member for contacting a second vertebrae and an intermediate member positioned between the first and second members. The assembly includes at least two bearing surfaces. A first bearing surface formed between the first member and the intermediate member and the second bearing surface formed between the second member and the intermediate member. At least one of the bearing surfaces is curved and at least one of the bearing surfaces is flat. The curved bearing surface can be spherical, cylindrical, ellipsoidal, oblong, etc.
In some embodiments, the curved bearing surface provides at least three degrees of rotational freedom. The linear bearing surface can provide at least two degrees of translational freedom and one degree of rotational freedom. The rotational and translational freedom of an IPD can also be selectively limited through arrangements disclosed herein.